Prior methods and apparatus of non-invasively measuring subjects optically are less than ideal in at least some respects. For example, prior methods and apparatus of measuring blood of a subject can be less accurate than would be ideal. Also, alignment of the subject with the measurement apparatus can be challenging. Many of the prior art spectrometers are less than ideally suited to measure constituents non-invasively in vivo. Although prior methods and apparatus may measure blood spectroscopically in a controlled laboratory environment, these methods generally involve the removal of blood from the subject, which can be inconvenient and somewhat painful in at least some instances.